Hurricanes captain Dane Coles has suffered an unexplained concussion while he was injured: Getty

New Zealand hooker Dane Coles is the latest injury concern for head coach Steve Hansen after the Wellington Hurricanes captain was diagnosed with concussion-like symptoms, despite not suffering an obvious blow to the head because he is already sidelined with injury.

The 30-year-old, widely regarded as one of the best – if not the best – No 2 in world rugby, has not played since the Hurricanes’ 45-15 victory over the Otago Highlanders on 18 March. Coles suffered a knee injury during the New Zealand division Super Rugby match, but has since also suffered a calf strain that hampered his recovery.

More alarmingly though, the Wellington head coach, Chris Boyd, confirmed that Coles is now suffering from “headaches” that leaves him battling to be fit in time for the visit of the British and Irish Lions tour this summer.

"Colesy's situation is complicated by the fact that... subsequent to his knee injury, he not only developed a calf strain but also some headaches," Boyd said on Wednesday.

"He is now under a return to play protocol for concussion.

"We genuinely don't know where he got those symptoms from," he added.

"We've had a look at the Highlanders game, which was the last game he played. He had no symptoms post that, so I'm not sure. The source of that is completely unknown to us."

Coles is highly unlikely to return for this Friday’s Super Rugby clash with South African side the Stormers, and he first reported the head issues when he stepped up his recovery in training, despite not suffering a blow to his head as he had not yet returned to full contact work.

"At the end of the day, he has started to return to train and developed some headaches," Boyd said.

"It's not normal, but if you look at it in context, because of his knee injury, the first part of his rehab was no training at all so, if there were symptoms post the game that would come out under exercise, they were not apparent."

All Blacks coach Hansen will be concerned with Coles’ setback, given he has also seen both captain Kieran Read and flanker Jerome Kaino suffer injuries over the last fortnight, with full-back Ben Smith and wings Israel Dagg and Nehe Milner-Skudder also currently sidelined.

Coles faces a race to be fit to face the Lions (Getty)

The Lions arrive in New Zealand at the end of the month before beginning their ten-match tour on 3 June, though the All Blacks do have the added benefit that they do not play their first Test against the Lions until 24 June, giving Hansen’s injured players more time to recover from their injuries.